As a method of encapsulation molding of a semiconductor device using an epoxy resin composition for encapsulating a semiconductor (hereinafter referred to as the epoxy resin composition or the resin composition), there has been generally used transfer molding using a tablet obtained by forming a solid epoxy resin composition in a cylindrical shape. However, in recent years, as a new molding method, there has been reviewed a compression molding method used for encapsulation. Since macro-flow of a molten resin in this compression molding method is smaller as compared to the conventional transfer molding, this method has been paid attention to as a method of minimizing wire sweep with respect to a semiconductor device in which a lead frame or a circuit board and a semiconductor element are connected by means of fine pitch wires, long wires, small diameter wires or the like.
As a technique relating to a semiconductor device obtained by encapsulating a semiconductor element by compression molding, there have been disclosed a method comprising encapsulating with a resin by compression molding while reducing the pressure in a mold (for example, refer to Patent Document 1), a method comprising using an encapsulation molding material having a thickness of not more than 3.0 mm in a pellet shape or a sheet shape (for example, refer to Patent Document 2), a method comprising supplying a granular resin composition into a cavity, melting the resin composition, immersing a semiconductor element therein, and curing the resin composition for encapsulating the semiconductor element (for example, refer to Patent Document 3), and the like.
One example of a method of encapsulating a semiconductor element using a granular resin composition by compression molding will be described in more detail with reference to FIGS. 1 and 2 illustrating a schematic diagram of a method of weighing of the granular resin composition and supplying it into a mold cavity. A granular resin composition 103 is conveyed in a predetermined quantity using a conveyance means such as a vibration feeder 101 or the like onto a resin material supplying container 102 equipped with a resin material supplying mechanism such as a shutter or the like capable of supplying the resin composition into a lower cavity 104 in an instant, whereby the resin material supplying container 102 containing the granular resin composition 103 is prepared (see FIG. 1). At this time, the granular resin composition 103 contained in the resin material supplying container 102 can be weighed by a weighing means arranged below the resin material supplying container 102. Next, the resin material supplying container 102 containing the granular resin composition 103 is arranged between an upper die and a lower die of a compression mold, and a lead frame or a circuit board on which a semiconductor element is mounted is fixed on the upper die of the compression mold by a fixing means such as a clamp, adsorption or the like such that a semiconductor element-mounted surface is directed downward (not illustrated). Further, when a lead frame or a circuit board is provided with portions piercing through, a surface opposite to the semiconductor element-mounted surface is subjected to lining using a film or the like.
Subsequently, when the weighed granular resin composition 103 is supplied into the lower cavity 104 by use of the resin material supplying mechanism such as a shutter or the like constituting the bottom surface of the resin material supplying container 102 (see FIG. 2), the granular resin composition 103 is melted in the lower cavity 104 at a predetermined temperature. Furthermore, after the resin material supplying container 102 is taken out of the mold, while reducing the pressure in the cavity as necessary, the mold is closed by use of a compression molding machine, the inside of the cavity is filled with the melted resin composition so as to surround the semiconductor element and the resin composition is further cured for a predetermined period of time, whereby the semiconductor element is encapsulated and molded. After elapsing a predetermined period of time, the semiconductor device is taken out by opening the mold. Incidentally, it is not essentially required to perform degassing by reducing the pressure in the cavity, but degassing is preferable because voids in the cured product of the resin composition are reduced. Furthermore, a plurality of semiconductor elements may be mounted on the lead frame or the circuit board, and may be laminated or mounted in parallel thereon.
In the technical field of such compression molding, there have been proposed a review of the particle size distribution (for example, refer to Patent Document 4), a review of resin properties (for example, refer to Patent Document 5) and the like, as a method to solve clogging or blocking (adherence) during conveyance, weighing or the like. However, it is not sufficient to solve the problem of productivity caused by uneven sprinkling, conveyance performance or the like, just by specifying the broad particle size distribution or selecting a resin hardly causing blocking. Further, in case that a resin is restricted to those which can be used in view of blocking, there have been problems such that the degree of freedom in formulation is low and the application range of the target semiconductor device is low.